Cleanup warnings 4 (#3013)

* Use InstanceKeyGraph instead of InstanceGraph
* Get rid of use of experimental.IO
* Symbol("s") instead of 's
* .toOption.get instead of .right.get
* No need to mix in AutoCloneType
* fromUnescaped instead of fir.StringLit
* MutableRenameMap instead of RenameMap
* Remove checkScalaVersion
* More use empty parens on method calls that need them
* getDeclaredConstructor().newInstance() not .newInstance()
* Erasure fixes
* () needed for some methods
* use object BackendUtilities
* use proper ChiselEnum
* use proper SourceInfo
* fix possible match errors
* use proper InstanceId
* use proper requireIsHardware
* processEscapes instead of treatEscapes
* use @nowarn() on things we are not able to fix in code at this time
  Add TODO comments to revisit these issues

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Co-authored-by: Jack Koenig <koenig@sifive.com>